Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$66.34	3.778%	$68.8463	$68.85	$68.85	$68.80
Purchase #2	$165.59	9.544%	$181.3939	$181.39	$181.40	$181.40
Purchase #3	$9.79	4.152%	$10.1965	$10.20	$10.20	$10.20
Purchase #4	$119.44	10.223%	$131.6504	$131.65	$131.65	$131.70
Purchase #5	$95.51	4.472%	$99.7812	$99.78	$99.80	$99.80
Purchase #6	$22.42	10.465%	$24.7663	$24.77	$24.75	$24.80
Purchase #7	$156.76	3.518%	$162.2748	$162.27	$162.25	$162.30
7 purchase totals =	$635.85		$678.9094	$678.91	$678.90	$679.00